introduction During the physical discharge of the tokamak plasma, the study of fracture and teeth is of great significance. Cracks and saw teeth are present during most tokamak discharges. Rupture is a notable event, during which the plasma constraints are severely damaged. Not only does it limit the operating area of ​​the plasma current and density, but also the mechanical stress and thermal load it causes bring serious to the plasma vessel wall damage. At present, there is still a lack of a detailed understanding of rupture in theory, which can be roughly divided into low-q rupture and density limit rupture. Using the Murugami parameter as the Hugill plot on the abscissa, we can get a first-hand understanding of the rupture and tokamak plasma operating area. In most cases, there is relaxation oscillation in the Tokamak plasma center, that is, sawtooth oscillation of temperature and density. During the rising period, the current density near the magnetic axis increases and the central q value decreases. During the descending period, the current density near the magnetic axis decreases and the central value increases. The mechanism of the sawtooth is not very clear, and it is generally explained by Kadamtsev's reattachment. The soft X-ray behavior of rupture and serration can be roughly divided into four stages, namely the prognosis period, the prognosis period, the rapid decline period, and the recovery or extinction period. For the rapid decline period of rupture and sawtooth, people usually misunderstand it, that is, during this period, the soft X-ray signal decreases monotonously or quasi-monotonically. In fact, as long as the sampling frequency is high enough, it is not difficult to find that soft X-rays are oscillating and that the first-order small quantity is greater than the zero-order quantity (usually the DC component is defined as the zero-order quantity). It can be seen that in order to obtain detailed information on cracking and sawtooth behavior, a plasma diagnosis method with a higher time resolution must be used. As the sampling frequency increases, the amount of data obtained also increases exponentially, which brings great difficulties to data storage, transmission and processing. To achieve high-speed data collection in the long discharge process, and complete the storage, transmission and processing of data within a given short time has become the key to the problem to be solved in the construction of the test system. Build VXI test system During the long physical discharge process of Tokamak plasma, cracking and sawtooth are very short-lived processes, which provides us with the conditions to overcome these difficulties. In this way, we compose a 40-channel VXI data acquisition test system. For the long discharge process, except for short-term processes such as rupture and sawtooth, its slowly changing characteristics use a lower sampling rate to collect the entire process data in each channel to ensure that it can collect To the data of the whole discharge process, it can meet the general test of the discharge process. Set its combat speed acquisition time to 1.6 seconds to cover all discharge processes. However, due to the low sampling frequency, the amount of data formed by the slow acquisition process lasting 1.6 seconds is only tens of K per channel. At the same time as the low-speed acquisition, each channel also has a high-speed acquisition parallel to the low-speed acquisition, which is specifically used to collect rupture and sawtooth events. High-speed acquisition and low-speed acquisition have different memories to store data. The high-speed acquisition memory is divided into many segments, which can be divided into 16 segments at most, and each segment of memory acquisition stores one burst and sawtooth event data. After the low-speed acquisition starts, a special event trigger module triggers rapid acquisition multiple times, and each trigger starts a rapid acquisition process to record an event signal. Due to the very short burst and sawtooth events, the duration is only a few milliseconds. For a high-speed 2MSa / s acquisition, the total length of each channel of the memory is less than 100K to meet the needs of multiple rapid acquisitions of stored data. In this way, the VXI test system we built uses a flexible way to realize the full picture of the long discharge process from low-speed acquisition, and to carefully analyze the short-term process of cracking and sawtooth from high-speed acquisition, and to judge the occurrence of events in At the moment of the discharge process, the memory requirement of about 3MSa per channel in the conventional way of collection was reduced to about 100KSa, which solved the contradiction that the amount of data generated due to the increase in sampling frequency increased exponentially. Provides a guarantee for the completion of data storage, transmission and processing in a given short time. Functional design considerations To build a test system, we first need a basic VXI platform: a 13-slot VXI chassis and a zero-slot controller. On the basis of this platform, we begin to build the test function part of this dedicated system. The hardware of the system test function part is abstracted into two basic functions: one is signal data collection and storage, including slow full-process acquisition and simultaneous rapid cracking and sawtooth event capture; the other is to identify and judge cracking and sawtooth Event, trigger the acquisition. Two abstract basic functions determine the two types of VX I modules to be developed by the test system: data acquisition module and event trigger module. In our test system, 40 parallel acquisition channels are required, and the data acquisition module is designed to have 4 channels per module, requiring 10 acquisition modules. 40 channels work in parallel. The rapid collection of the system only needs to be started by an event trigger module, and only one signal of the monitored channel needs to be discriminated to generate actions. The 13-slot VXI chassis is just right for use. The system working mode is carried out in this way: when the work starts, the event trigger module first receives the external trigger signal representing the start of the discharge process to start the slow acquisition of the data acquisition module, and at the same time starts the internal triggering module for the identification of cracks and sawtooth events. Whenever the event trigger module identifies the set event, it immediately sends out a trigger signal through the TTLTRGn line to start a fast data acquisition of the data acquisition module to capture the event signal of rupture and sawtooth. The occurrence of rupture and sawtooth events until the event trigger module identifies the event and there is always a delay when the trigger signal is given. Therefore, in the stored data corresponding to each rapid data acquisition, the negative delay trigger function must also be used. Once a quick data acquisition is completed, it automatically enters the next section of memory, ready to accept the next trigger, and start the next acquisition until the set number of fast data acquisitions is completed. Finally, when the data collection module's 1.6-second slow data collection process is completed, the entire collection process is declared complete before data processing can begin and prepare for the next work.
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